Conventionally, gaseous fuels in a pressure vessel, commonly known as a "cylinder", is supplied to a household heating device or recreational vehicle merely through a cylinder valve connecting a male fitting. This prior art has many disadvantages. Thus, an improved cylinder valve insert has been developed. The most market successful cylinder valve insert is disclosed in U.S. Pat. No. 5,330,155 to Lechner, issued on Jul. 19, 1994, which is incorporated herein as a reference. Although this prior valve insert can effectively achieve its intended functions, it still has some disadvantages. Among these disadvantages is that (please refer to FIGS. 3 and 4 of the '155 patent) due to the arrangement of the prior insert 40, when the male fitting 54 is screwed onto the cylinder valve 41, the nipple 52 firstly pushes the docking member 59; then, via the docking member 59, the nipple 52 pushes the valve member 58 in a leftward direction to overcome the biasing force produced by the spring 97 to release the sealing achieved between the seal 80 and the seat 72. In this arrangement, after repeated connection and disconnection of the cylinder valve 41 and the male fitting 54, the strength of the spring 97 may be weakened with a result that before the nipple 52 can hermetically engage with the docking member 59, the nipple 52 may have already pushed the valve member 58 in a leftward direction to release the sealing achieved between the seal 80 and the seat 72. In this situation, a leakage of gas may occur between the nipple 52 and the docking member 59. Furthermore, due to the nipple 52 needing to axially push the docking member 59 to move in a leftward direction, the front end face of the nipple 52 will exert a concentrated force on the docking member 59, which causes the docking member 59 to be locally subjected to a large stress, as a result the resilience of the docking member 59 will locally degrade quickly. Therefore, a frequent replacement of the docking member 59 is required.
In view of the above said disadvantages of the '155 patent, the present invention is disclosed to have a cylinder valve insert wherein the hermetic engagement between the docking member and the nipple will not be affected due to the decreasing of strength of the spring. In addition, the nipple of the present invention does not push the valve member via the docking member. Furthermore, the nipple will not exert an axially concentrated force on the docking member. Moreover, the present invention also discloses an embodiment which constructs the valve insert as a separated unit from the cylinder valve and can be easily and firmly mounted onto the latter.